1. Field of the Invention
This invention relates to the air brake systems of railroad freight trains and especially to devices for indicating the location of unwanted air brake leaks.
2. Discussion of Related Art
The standard air brake system of a railroad freight train operates in conjunction with a controlled source of air pressure furnished by a compressor system on the locomotive. Air at regulated pressure is supplied from the locomotive to each car coupled within the train by means of a brake pipe which extends the length of each car. Flexible hoses are provided at the ends of each car and equipped with on/off valves. Flexible hoses at the ends of each car are coupled manually to like hoses on the next car. The flexible hose at the rear of the last car is supported, and the air valve or angle cock is closed to prevent escape of brake pipe supply air pressure to atmosphere. All other air valves or angle cocks are positioned fully open to allow air pressure supply from the locomotive to be present throughout the total length of the brake pipe system.
A branch pipe is connected to each car into the brake pipe with a tee connection. The branch pipe conducts brake pipe supply air to and from the air brake system which consists of valvular portions, reservoirs, air cylinders and a system of rods and levers to transmit force to the brake shoes and hence to the car's wheels.
After the air brake system in each car is fully charged to a predetermined and regulated pressure, the brakes on each car can be operated in response to brake pipe supply pressure changes. When the locomotive operator reduces the brake pipe pressure at a controlled rate, the brakes on each car will apply at a controlled rate and in proportion to the reduction. When the locomotive operator restores the brake pipe pressure to the original regulated value, the brakes on each car will release.
Should the locomotive operator reduce the brake pipe pressure at a rapid rate, the brakes on each car will apply at a faster rate and the total braking force will be increased over normal service braking. As in serivce braking, release of the brakes is accomplished by restoration of the brake pipe pressure to the original regulated charge level. Release of the brakes, following a rapid or emergency application usually requires a longer period. All of this is well-known by train operators and technical maintenance personnel in the railroad industry. The air brake system will operate to apply brakes at each car in the event that the brake system regulated pressure is affected by a leak in the system. Should a leak occur in the system, such as at a loose fitting gasket, flexible hose, or any leak source greater than the capacity of the locomotive regulated air supply, the brakes at each car will operate automatically. Should a sudden leak occur at a rapid rate, the brakes on each car will be automatically applied into emergency application.
Such a rapid lead in the brake pipe system can result from a separation of the brake pipe system, as in the case of the train coming uncoupled, a separated or burst hose or pipe and/or a malfunctioning air brake valvular portion. When the brakes of a train are applied in an emergency, other than when deliberately applied by the locomotive operator, such a brake application is called an "Undesired Emergency Application".
In the event that a train experiences a separation, the source of the brake pipe system opening is readily apparent. Also, if a hose separates or bursts or any other visual leak occurs, the source can be identified upon inspection of the train and repairs can be effected. In the case of a malfunctioning valvular air brake equipment portion on one or more cars being responsible for the undesired emergency brake application, the problem of identifying the particular car or cars is difficult and time consuming and contributes to excessive train delays. Such a malfunctioning valvular portion may repeat the malfunction periodically during train operations, thereby creating a series of repeated undesired emergencies when the brakes have been released and train operation is resumed.
The usual method employed by train crewmen to locate a particular car with a malfunctioning valvular portion is a time consuming process whereby blocks of cars are tested in order to pinpoint the defective car or cars.
U.S. Pat. No. 3,807,808, issued Apr. 30, 1974, to Souther illustrates a typical system, for locating air leaks. The Souther system comprises pressure actuated counters in the first and last cars of a train. Upon an undesired emergency brake application, each counter is activated when a decrease in pressure advances serially through the cars and reaches the counter. The time differential of initiation of the counters is used to determine the location of the leak.